The presence of toxic Heavy Metals and Metalloids (HMM) in the environment greatly affects the quality of water, soil and chain-food. The toxicity of the HMM depends on metal availability. Many analytical methods, such as sequential extraction or mathematical modelling, have been used for a long time for the assessment of HMM bioavailability. However, these techniques are very often difficult, expensive and long. The biosensors, like analytical tools, have advantages while bringing in addition to specificity, fast and quantitative measurement of a metal that reacts with the biomaterial. This principle is applied to detect the presence of bio-available concentrations of certain metals. The biosensor presented in this study is an amperometric one and its sensitive part is a hemo-protein, the cytochrome c3 from Desulfomicrobium norvegicum. The cytochrome c3 has been chosen for its better properties as a reducing agent of chromate (CrO42-). This study required instrumental developments or adaptations: the development of glassy carbon electrode with immobilized cytochrome c3 and the implementation of electrochemical methods for the study of redox systems, i.e. cyclic voltammetry (CV) and chronoamperometry (CA). The performances of various configurations of biosensors, according to the mode of immobilization of the enzyme, are studied for the qualitative and quantitative determination of chromate. These tools made it possible to identify and follow the redox reactions taking place during the contact of the electrode without and with chromate in solution. The tests on the various configurations of electrode allowed us, for the moment, to choose two promising configurations: The first one is an immobilization of the enzyme with a dialysis membrane and the second is an immobilization with a cellulose nitrate filter. Chromate concentrations from 0.2 to 6.8 mg/L can be detected by the biosensors that were designed.